booklet 3 - the drainage basin

• What is a drainage basin?

  The area that supplies a river with water
• How are drainage basins separated?

  By high land
• What is the source of a river?

  Where it starts
• What is the mouth of a river?

  Where the river meets the sea/lake
• What is a tributary?

  Small streams/rivers flowing into a larger river
• What is a confluence?

  Where two rivers meet
• What is a watershed?

  Edge/boundary of the drainage basin
• What are the components of drainage basins?

  • Inputs: Precipitation
  • Outputs: Transpiration, Evaporation
  • Storage: Surface, Soil, Groundwater, Vegetation, Channel
• What happens to water during storms in drainage basins?

  More rainfall increases water in stores
• How does heavy rain affect surface runoff?

  Heavy rain causes increased surface runoff
• What is the effect of deforestation on drainage basins?

  Less trees lead to less interception
• How does urbanization affect drainage basins?

  More buildings increase surface runoff
• How do seasonal changes affect drainage basins?

  They interrupt water transfers and storage magnitude
• What is the impact of farming on drainage basins?

  Irrigation diverts water from rivers
• Why is vegetation cover important in drainage basins?

  It stores precipitation as interception
• How much rainfall do pine forests intercept?

  28% of rainfall
• How much rainfall do deciduous forests intercept?

  19% of rainfall
• How much rainfall do tropical forests intercept?

  58% of rainfall
• What is the link between groundwater flow and baseflow?

  Baseflow comes from groundwater storage
• What happens if rainfall intensity exceeds infiltration rates?

  Water becomes surface runoff
• What controls the rate of infiltration?

  Gravity, capillary action, soil porosity
• How does soil texture affect infiltration rate?

  Coarse soils allow greater water flow
• What happens to infiltration rate during a rainfall event?

  It initially increases, then stabilizes
• What is the water balance?

  The balance between inputs and outputs
• What indicates a positive water balance?

  Precipitation exceeds runoff and evapotranspiration
• What indicates a negative water balance?

  Runoff and evapotranspiration exceed precipitation
• What does the equation P = O + E - S represent?

  Water balance equation
• What is soil moisture deficit?

  Water removed from soil in summer
• What is soil moisture surplus?

  High precipitation with low evapotranspiration
• What are the ways in which overland flow occurs?

  • Saturation excess overland flow
  • Rainfall intensity exceeds infiltration rates
• What happens when soil is totally saturated?

  Extra rainfall flows over the soil surface
• What occurs when rainfall intensity exceeds infiltration capacity?

  Water becomes surface runoff